What is LCD screen light leakage?
Date:2025-12-10
What causes LCD screen light leakage?
The fundamental reason for light leakage in LCD screens lies in their physical structure and working principle: LCD itself does not emit light and must rely on a backlight system to provide illumination. Leakage is essentially the escape of light from the backlight source to the display area that should be completely dark. This is mainly caused by technical limitations, manufacturing accuracy, material properties, and usage environment.
The following are the detailed reasons for LCD screen light leakage, from core design to specific steps:
1. Congenital design limitations (technical roots)
This is the fundamental reason, determined by the type of backlight.
Structural defects of side entry backlight:
Principle: Light enters the light guide plate from the side and needs to be precisely guided and scattered throughout the entire screen. This process itself is indirect and indirect.
The inevitable result is that at the edge of the screen (near the LED light bar), the light intensity is naturally the strongest. Even with good light guide plates and optical films, it is difficult to achieve absolute uniformity from the edge to the center, resulting in edges being "brighter" than the center and appearing as edge leakage or "halo" in black images. This is the inherent cost that side entry pays for pursuing slimness.
Limitations of direct backlight and zone controlled lighting:
Direct lighting without partition control: Although the light is uniform, the entire backlight is a whole, and when black is displayed, the backlight is still bright, and the entire screen will present a uniform gray white color (which can be considered as full screen light leakage).
Direct type with partitioned light control: Although the backlight in dark areas can be turned off, there is still slight lateral scattering of light in the diffuser plate and prism film. When a partition lights up and adjacent partitions need to be turned off, light may "overflow" to the closed partition, forming a halo. The fewer the number of partitions, the larger the area of a single partition, and the more obvious the halo phenomenon.
2.Variables in the manufacturing and assembly process (key to quality control)
Even with the same design, slight differences in the production process can lead to varying degrees of light leakage.
Quality and process of light guide plate and optical film:
Uneven design/carving of scattering dots on the light guide plate can lead to local focusing or uneven brightness.
Scratches, contamination, or uneven material of diffusion films and brightening films can also affect the path of light and produce bright spots or dark spots.
Assembly accuracy and tolerance:
The adhesion between the frame and the panel: The metal or plastic frame of the screen is pressed together with the LCD panel, optical film, and backlight module through buckles and adhesive strips. If the pressure is uneven during assembly, there are gaps in the rubber strip, or there is slight deformation in the frame, a "gap" will be formed at the joint, and light will directly leak out from there, forming a clear edge beam. This is one of the most common and frustrating forms of light leakage.
The alignment of each layer component is not accurate: there is no perfect alignment between the LCD panel, optical film, light guide plate, and LED light strip, causing the light to take a shortcut.
Characteristics of LCD panel itself:
Panel type: IPS panels, due to their arrangement of liquid crystal molecules, cannot completely block light when displaying black like VA panels, resulting in lower native contrast and more noticeable backlight leakage visually (black is not black enough, making the leakage appear brighter).
Panel uniformity: The slight differences in light transmittance in different areas of the panel may also exacerbate the unevenness of light leakage.
3.Physical stress and environmental factors (postnatal triggers)
External pressure and deformation:
Improper installation: The wall bracket is tightened too tightly, or the base is installed improperly, causing sustained pressure on a certain part of the screen.
Squeezing or collision during transportation or use: causing slight deformation of the screen frame, internal skeleton, or light guide plate, resulting in new light leakage points or exacerbating existing light leakage. This is also why light leakage detection is important when opening a new device.
Thermal expansion and contraction:
The screen will generate heat after prolonged operation, and the internal components will slightly expand. After shutting down and cooling down, it will shrink again. Long term cold and hot cycles may cause micro gaps in the originally tight joints or alter internal stress, resulting in slow changes in light leakage over time.
Material aging:
The rubber strips and gaskets used for bonding and sealing may age, harden, and lose their elasticity over time, resulting in a decrease in sealing performance and possible worsening of light leakage.
Summary: Understanding the causes of light leakage with a single image
Reason category | Specific factors | Resulting in light leakage characteristics |
Design limitations | 1. Side entry backlight structure | A uniform "halo" around the edges of the screen, with brighter corners or sides. |
2. Insufficient number of direct partitions | A blurry "halo" phenomenon appears around bright objects. |
Manufacturing and Quality Control | 1. Defects in light guide plate/optical film | Abnormal bright spots, lines, or dark areas appear locally on the screen. |
2. Poor assembly and gaps in the frame | Obvious and asymmetric edge beams (often appearing at corners). |
3. Poor uniformity of the panel | The overall or partial black and gray hair is uneven. |
Postnatal factors | 1.External pressure/deformation | New and concentrated areas of light leakage appear at or around the pressure point. |
2. Thermal expansion, contraction, and material aging | The range or degree of light leakage gradually increases over time. |
Popular understanding:
You can imagine the LCD screen as a 'multi-layer sandwich':
The backlight is a flashlight.
Light guide plates and optical films are frosted glass and lenses responsible for transforming point/line light into uniform surface light.
The LCD panel is responsible for opening and closing the blinds of each pixel.
The screen frame and adhesive strip are the shell and sealing strip that press everything tightly.
Leakage refers to the light from a flashlight that has not been 100% homogenized by frosted glass or has escaped through poorly sealed gaps in the casing. Poor quality, rough workmanship, and loose "shell" of "frosted glass" can all lead to more light "escaping".
Therefore, it is impossible to completely eliminate light leakage from LCD screens, which is determined by their physical structure. What we can do is to control it at a level that is difficult to detect with the naked eye in daily use through sophisticated design (such as Mini LED multi zone), rigorous manufacturing and assembly. When light leakage manifests as severe asymmetric beams or bright spots, it is usually a quality control issue and should consider contacting after-sales service.
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